A vehicle equipped with an internal combustion engine and automatic transmission which provides motive torque to a driveline typically employs a torque converter device having a lock-up device referred to as a torque-converter clutch (‘TCC’). The typical torque-converter clutch comprises a fluid-operated friction device which, when fully actuated, mechanically couples an input impeller and output turbine of a torque converter, to permit transmission of torque therebetween. The input impeller is typically mechanically attached to a crankshaft of the engine, and the output turbine is typically mechanically attached to an input shaft of the transmission.
When the torque-converter clutch is fully actuated, engine torque perturbations can be passed directly to the vehicle driveline and hence to the vehicle. Vehicle calibrators typically generate torque-converter clutch apply/release calibrations, referred to as maps, that minimize driveline disturbances, referred to as NVH for ‘noise, vibration, and harshness’. TCC apply-release maps are typically calibrated using operator input of either accelerator pedal position or throttle position (‘TPS’), and, vehicle speed. When TPS and vehicle speed are used as calibration inputs, opportunities to apply the torque-converter clutch are typically not maximized, because some TPS values result in both acceptable and unacceptable levels of NVH, depending on engine speed and load. When the TPS and vehicle speed are used as calibration inputs, a single unacceptable NVH condition at a given TPS and vehicle speed effectively prevents applying the torque-converter clutch at all load conditions at the specific TPS/vehicle speed point.
Some vehicle systems implement hybrid powertrain systems which provide motive torque from the internal combustion engine, and are able to utilize stored electrical energy to assist vehicle operation to obtain benefits related to reduced fuel consumption and reduced exhaust emissions. One such system is an Engine Stop-Start (ESS) system, which uses many conventional powertrain components and subsystems, and implements engine fuel cutoff and engine stop events during occurrences of decelerations and vehicle stops. The engine is subsequently restarted when the vehicle operator so commands. One exemplary ESS system relies upon a high-voltage battery system, a power inverter and a motor-generator to provide ESS functionality.
Hybrid vehicle systems, including the ESS system, must ongoingly re-energize the vehicle electrical energy storage devices, which typically include high voltage battery systems or other electrical energy storage devices. Re-energizing the electrical energy storage devices can take the form of regeneration events, wherein electrical energy is derived from vehicle kinetic energy, and charging events wherein electrical energy is derived from vehicle engine power. Energy for charging typically comes from torque caused by engine rotation which drives an electric machine, i.e. a generator, which is operable to generate electrical energy for storage in the electrical energy storage device. Energy for regeneration typically comes from regenerative braking, wherein vehicle kinetic energy is captured by causing the driveline to transmit torque through the powertrain to the electric machine.
Electrical energy captured during regenerative braking is confined to that torque which can be transmitted through the entire powertrain to the electrical machine, which means an operating range in which the torque-converter clutch is in a lock mode or a controlled-slip mode. Referring now to FIG. 2, Line A shows a typical shift point from second to third gear of a four-speed automatic transmission, based upon vehicle speed and throttle position. Line B represents a typical operating line for torque-converter clutch actuation based upon vehicle speed and throttle position for third gear. In the operating region to the right of line B, the torque-converter clutch is applied. In the operating region to the left of line B, the torque-converter clutch is open, or unlocked, and regenerative braking is disabled. As can be seen, there is a substantial operating region between Lines A and B in which the vehicle may operate, but in which regenerative braking may not occur due to limitations related to NVH and other concerns.
There is a need to increase operating region of a torque-converter clutch on a vehicle employing regenerative braking in order to obtain the benefits thereof, without compromising vehicle NVH and other driveability concerns.